The invention relates to a method for separating out individual sheets from a sheet-processing machine, in particular, at the delivery of a printing machine with pile or stack formation, by a revolving gripper chain having gripper bars extending transversely to the sheet conveyance direction, and grippers which are arranged on the gripper bars and successively grip the sheets at the leading edge thereof and convey them to a stacking or pile region to be deposited, whereat, in order to separate out the sheets, they are conveyed over and beyond the stacking or pile region and, at a predefinable location, are transferred to a separating device having a controllable revolving suction belt for braking and separating out the sheets.
In order to assess or evaluate the printed image in a printing machine, individual printed sheets, so-called proofs, must be removed at regular intervals during progressive operation. In the case of stack-building or pile-forming printing machines, these proofs have heretofore been removed manually from the progressively forming stack or pile.
German Patent 195 19 374 describes a device for automatically separating out individual printed sheets with the aid of a second separating device arranged behind the stacking region and serving for conveying an incoming sheet out of the delivery of the machine and depositing it on an extensible table. The desired sheets are drawn beyond the stack region to the aforementioned second separating device by a gripper chain revolving continuously at the machine cycle rate in order to convey the printed sheets, and are transferred, at the second separating device, to a revolving suction belt, instead of being deposited on the sheet pile as usual.
Through the intermediary of the revolving suction belt, the sheets are braked to an output speed. In the course of the braking, the sheets behave differently, depending upon the stiffness of the paper, and the machine speed. Failures or faults occur because of sheets entrained by the grippers, as well as due to collisions with succeeding sheets at high machine speed.
It is accordingly an object of the invention of the instant application to provide a method of separating out individual sheets in a printing machine, which functions reliably and irrespectively of the paper being processed and the speed of the machine.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for separating out individual sheets from a sheet-processing machine, by a revolving gripper chain having gripper bars extending transversely to a direction wherein the sheets are being conveyed, and grippers arranged on the gripper bars for gripping the sheets one after another at a leading edge thereof and conveying them to a stacking region for deposition, whereat, the sheets to be separated out are conveyed over and beyond the stacking region and, at a predefinable location, are transferred to a separating device having a controllable revolving suction belt for braking and separating out the sheets, which comprises bringing the suction belt to sheet speed, picking up with the suction belt a respective sheet to be separated out, and opening the grippers, somewhat braking the suction belt briefly and, after withdrawal of the respective sheet from the grippers, accelerating the suction belt again to at least the previous speed thereof, and outputting the respective sheet while it is being braked.
In accordance with another mode, the method of the invention for separating out individual sheets, includes performing the separation at a delivery of a printing machine capable of sheet pile formation.
In accordance with a further mode, the method of the invention includes, after the respective sheet has been withdrawn from the grippers, accelerating the respective sheet beyond the original speed thereof, and reestablishing the original travel spacing of the respective sheet from the next following sheet before braking the respective sheet.
In accordance with an added mode, the method of the invention includes, after the respective sheet has been withdrawn from the grippers, accelerating the respective sheet beyond the original speed thereof, and moving it farther away from the next following sheet a spaced distance greater than the spaced distance originally therebetween, and then outputting the respective sheet while it is being braked.
In accordance with an additional aspect of the invention, there is provided a method for separating out individual sheets from a sheet-processing machine, by a revolving gripper chain having gripper bars extending transversely to the direction in which the sheets are being conveyed, and grippers arranged on the gripper bars for gripping the sheets one after another at a leading edge thereof and conveying them to a stacking region for deposition thereat, further conveying the sheets to be separated out, over and beyond the stacking region and transferring the sheets, at a predefinable location, to a separating device having a controllable revolving suction belt for braking and separating out the sheets, which comprises, upon the arrival of a sheet to be separated out, bringing the suction belt to sheet speed, applying suction by the suction belt to the sheet, opening the grippers, accelerating the suction belt to a higher speed, after releasing the sheet from the grippers, and then outputting the sheet while braking the sheet.
In accordance with yet another aspect of the invention, there is provided a sheet-processing machine capable of sheet stack formation, having a device for separating out individual sheets by a revolving gripper chain having gripper bars extending transversely to a sheet-conveyance direction, and grippers arranged on the gripper bars for gripping the sheets one after another at a leading edge thereof and conveying them to a stacking region for deposit thereat, the sheets to be separated out being conveyable over and beyond the stacking region and, at a predefinable location, being transferrable to a separating device having a controllable revolving suction belt for braking and separating out the sheets, comprising equipment for bringing the suction belt to sheet speed, for causing a sheet, that is to be separated out, to be picked up by the suction belt, for opening the grippers, for braking the suction belt briefly, and for accelerating the belt again to at least the previous speed thereof, after the sheet has been withdrawn from the grippers, and for finally outputting the sheet while braking it.
In accordance with yet a further aspect of the invention, there is provided a sheet-processing machine capable of sheet stack formation, having a device for separating out individual sheets by a revolving gripper chain having gripper bars extending transversely to the direction in which the sheets are being conveyed, and grippers arranged on the gripper bars for gripping the sheets one after another at a leading edge thereof and conveying them to a sheet stacking region for deposit thereat, the sheets to be separated out being conveyable over and beyond the stacking region and, at a predefinable location, being transferrable to a separating device having a controllable revolving suction belt for braking and separating out the sheets, comprising equipment by which, upon the arrival of a sheet to be separated out, the suction belt is bringable to sheet speed, for causing the sheet to be picked up by the suction belt, for opening the grippers, for accelerating the suction belt to a higher speed, after releasing the sheet from the grippers, and for finally outputting the sheet while braking it.
In accordance with a concomitant feature of the invention, the sheet-processing machine is a rotary printing machine, and the device for separating out individual sheets is located at a delivery of the rotary printing machine.
When a stiff paper quality is being used, the aforestated object of the invention is readily achievable. However, when stiff paper is being processed, jamming of the sheets in the already opened grippers can occur, so that the sheets are not released from the grippers, which results in the sheets being drawn into the machine again. As a result of the brief braking of the suction belt, the sheets are drawn out of the grippers. In order not to collide with the next following sheets, however, the respective sheet released in this manner must be transported onward by the belt without any delay and at normal speed, and finally separated out. For this purpose, the belt is accelerated again to the original speed thereof. The sheet can finally be deposited on a shelf secured to the outside of the machine delivery, or else in a tray, and can be removed.
In order to ensure a smooth operation when removing a proof, even at high machine speed, provision can be made for the sheet, after being pulled out of the grippers, to be accelerated beyond the original speed, and the original spacing thereof from the next following sheet during travel to be reestablished before the sheet is braked. In this way, the loss in terms of distance which the sheet has experienced with respect to the next following sheet as a result of the brief braking is compensated for again. The situation is therefore avoided wherein the next following sheet runs onto the separated-out sheet at high machine speed.
In order to separate a number of successive sheets of heavy paper (above about 240 g/m2), for each of the sheets to be separated out, provision can be made for the sheet, after being pulled out of the gripper, to be accelerated beyond the original speed, and to be moved further away from the following sheet than was originally the case, and for the sheet to be finally output while being braked. As a result of the brief braking, the distance from the following sheet is reduced, is compensated for again by the acceleration beyond the original speed and is further increased beyond the original value. In this way, it is possible for a number of heavy sheets to be removed one after another without any collisions occurring.
In order to separate out a number of successive sheets of lightweight paper (up to about 240 g/m2), and in order to achieve the object of the invention, for each of the sheets to be separated out, provision can be made that, upon the arrival of a sheet to be separated out, the suction belt be brought to sheet speed, that the sheet be picked up by the suction belt and the grippers be opened, that the suction belt, after detaching the sheet from the grippers, be accelerated to a higher speed, and that the sheet be finally outputted while being braked. As a result of the extra increase in the speed, a spaced distance from the next following sheet can be built up, which permits the reliable braking and removal of the sheet before the next sheet is delivered to the separating device.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for separating out individual sheets in a printing machine, and a device for performing the method it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.